UPDATE: I have added new info at the bottom of this post with more commentary from AMD (kind of).

You might have seen some reports in the last couple of days claiming that the upcoming Sony PlayStation 4 (PS4) will have a big advantage over the Xbox One thanks to its unique ability to support AMD's hUMA memory architecture. hUMA, heterogeneous unified memory architecture, is an exciting new memory technology that AMD has built into upcoming APUs.

The idea behind hUMA is quite simple; the CPU and GPU share memory resources, they are able to use pointers to access data that has been processed by either one or the other, and the GPU can take page faults and not rely only on page locked memory. Memory in this case is bi-directionally coherent, so coherency issues with data in caches which are later written to main memory will not cause excessive waits for either the CPU or GPU to utilize data that has been changed in cache, but not yet written to main memory.

There's just one problem with these various reports (VR-Zone, ExtremeTech): they're incorrect. After sending some emails to our representatives at AMD I was told that "Kabini doesn't support hUMA" which is the APU that both the PS4 and Xbox One processors are based on. AMD further clarified with us:

Our spokesperson made inaccurate statements about our semi-custom APU architectures and does not speak for Microsoft, Sony or the AMD semi-custom business unit responsible for co-developing the next generation console APUs.

So while the PS4 will still be a faster system thanks to its higher SIMD processor (GPU core) count, there is no support for a true heterogeneous unified memory architecture in either upcoming console platform.

NOTE: I have had several people point out that it's possible Sony and Microsoft worked on their own custom memory architectures that will perform similar functionally to hUMA. That is entirely possible but means that official hUMA support isn't on the SoCs.

UPDATE: AMD contacted me again to make another comment. Essentially, they said that the correction statement to the original statement claiming hUMA was part PS4 was "inaccurrate" but that this correction does NOT mean the opposite claim is true. Even when pressed for a more specific and debate-ending comment, AMD wouldn't give us any more information.

So does the PS4 have support for some type of heterogeneous unified memory? Maybe. And the Xbox One? Maybe. At this point, I'd stop listening to anything AMD has to say on the subject as they are likely to recant it shortly thereafter. Many readers have emailed me with their thoughts and I personally feel that its more likely the original statement from AMD (that the PS4 will have the edge with a hUMA design) will turn out to be the truth in the long run...

Of course it will be easier. Just because PC is traditionally doing it the hard way does mean implementing unified memory using will be difficult. The devs know what they want to make life easier. It was them that specifically asked for unified memory to make life easer. That fact blows you're argument out of the water.

Actually there is always a lead platform in game development. Originally with PS3 and Xbox 360 the lead platform was Desktop PC's. But later the PS3 became lead platform for certain games because Sony themselves owned or had partnered with so many developers during the PS2 years. Which was the largest game selling platform in the World.

But what both you and this writer doesn't seem to be aware of is that Sony is a member of HSA governing board and Microsoft is NOT. So the chance of HSA being used by Sony is far greater than Microsoft and they most likely wouldn't have the latest version anyway.

So cross platform is never simultaneous in reality. But the main thing I want to point out is that AMD/ATI have been working on a deal with Sony as a co-member of HSA to push PS4 as lead developer platform for their HSA Gaming platform. This would accomplish several things. First by providing Sony an edge in the console wars and giving AMD/ATI the gaming edge on Desktops. If the games are all written with HSA, then they can actually be ported to desktops too. Since Sony is more into competing against Microsoft and Intel, they won't mind being able to easily port games to desktops too!

If what Sony and AMD/ATI have planned pans out, Microsoft Xbox and their so called lock on Desktop games for Windows Game computing will be in grave jeopardy. Because will be platform locked where full porting is required and the Sony AMD/ATI cross platform development will mean even AMD/ATI's Desktop SoC chips will become far more attractive to developers too. As it is now, the competition has to rely on full porting and recoding from one platform to another.

Whereas with Sony now willing to drop big name PS4 games onto the desktop gamer market, that can't be so easily ported over to the MS DirectX API's as Intel/Nvidia games. Both AMD/ATI and Sony benefit from a major HSA on both Desktops and PS4 would steal basically all of the competition's thunder by getting some really great games that MS DX guys would be losing. No doubt many gamers will love playing some exclusive Sony games on their Notebook and home computers too!

It doesn't exactly work that way. One of the chief differences between the Console and PC market is the Operating System itself. The OS inside a Console is specifically tuned for optimum gaming performance, and direct hardware access (I assume) there are not the same OS bottlenecks that Windows will give you.
It's why an Xbox 360 can look relevant 8 years after it launched without changing it's graphics hardware.

To some degree, staying within x86 architecture makes the game easier to port, but only so much, if the OS is still completely different, and I expect that it is. Else the graphics & gameplay would get worse, rather than better, when additional features are added. A big benefit though it should make emulating the console itself much easier.

A console plays games as a standalone for a reason, it isn't expected to do as much as Windows does in the background, but it is getting there. It doesn't have to concern itself with supporting driver updates, and for that driver to support several dozen cards before it.
It doesn't have to worry about print-spoolers or even virus protection to any real degree. A console is more of a single-purpose embedded media appliance than a PC, even though the hardware is identical.

Why a stand-alone 'gaming OS' hasn't been developed for PCs, even as an experiment, is beyond me.

AMD merely states Kabini doesn't support hUMA, not that the PS4 doesn't support hUMA. Customizations do not preclude hUMA support. We know the PS4 APU customizations (Garlic/Onion) fulfill the criteria for supporting hUMA.

The clarifications/retractions from AMD about a certain recent comment is a PR dance to avoid damaging one platform already dealing with an epic PR mess on its hands.

Saying "Kabini doesn't support hUMA" is one thing, and accurate; a vanilla Kabina design simply doesn't support the feature.

Saying Kabini *based* designs do not support hUMA is entirely different; it is definitive and implies no level of customization will yield that feature. We know this can not be the case given the published technical specs on the PS4 APU and interviews thus far.

It's obvious given what Diana said is bad PR for one of their very own big clients potentially affecting a multi-billion dollar business before the product is even out the door. AMD's official policy is not to comment or more importantly compare these platforms. AMD's quote doesn't actually refute anything - it's a retreat to a neutral stance. Their calling Diana's comment inaccurate just means it doesn't reflect their official stance, not that he was wrong about anything.

You are correct. But I was told that Kabini-based designs weren't to have hUMA support. Take that for what you will and as I added to the post its possible that a less specific unified memory design could be implemented by either party.

Kabini is a SoC without huma, consisting of 4 Jaguar cores, 2 MB L2, a 2 memory controller for GPU/CPU, one DRAM controller for single channel DDR3, a small GPU and various I/O stuff (PCIe, USB etc.).

Now the only thing we know about the PS4's architecture is, that it is based on Jaguar cores, too. There is no direct connection to Kabini. We dont know anything about the uncore part of the chip.

Crucial for huma is having just one memory controller for both GPU and CPU, that's where the memory addresses are coming from. AMD developed this for Kaveri. I dont see any problem why AMD would not be able to bolt together some Jaguar cores plus their Kaveri-huma-uncore for Sony's PS4 SoC.

In short:
Kabini is not Jaguar and especially not PS4
PS4 uses Jaguar and an unknown uncore
Huma is an uncore feature
oh and ... Sony is a member of the HSA foundation, I guess they'll need membership for a new Walkman. ;-)

Less specific? I don't have any idea of what you're trying suggest, because with something like Heterogeneous computing that AMD has been working on since buying ATI, it can't be associated with HSA by any other name or process uHUMA. It either is or it isn't and with Sony as an HSA Foundation contributor, why would you doubt the fact that their own Premier Next Gen Game Console wouldn't be HSA compliant in the first place? ah.... a Microcrud defender I see!

Just like with IBM designing the chips for both 360 and PS3, they never took sides on which was better. It would be suicide to do otherwise. Now the real company you needed to push was Sony. Because just like with PS3 they are obviously hiding features not revealed until it was actually in consumer's hands. But we already know the answer would be to only say what that is after the PS4 launches!

Does your website have a contact page? I'm having a tough time locating it but, I'd like
to shoot you an email. I've got some suggestions for your blog you might be interested in hearing.
Either way, great website and I look forward to seeing it expand over
time.

ps4 will most probably support huma
here are some facts however:
the employee that made the statement wasnt authorized to reveil any info about hUMA, nor is any other amd employee, because it violates the contract between microsoft and amd, and also between amd employees and amd. They had to cover it up because it would cause people to turn away from xbox.
Amd HAD NOT made any OFFICIAL PUBLIC statement where they deny that hUMA is indeed in PS4.
Kabini is term that is used for multiple chips, some support huma some not.
BTW nice seeing you on the wan show, hope for more.

Plus during the arch panel, MS stated the xbox1 would bring hardware coherency to a gpu on a massive scale.

I find it hard to believe that two console companies would pay billions of dollars to AMD and then allow AMD to keep part of its tech away from those companies especially when one of those companies is MS. Whose relationship in the console space has existed since before 2005. And who relationship in the x86 space with Windows has existed for far longer.

Furthermore, x86 and PC gpus is not something MS is naive about nor is heterogeneous computing. You only have to look at the work of MSR and its collaborators to see how deeply MS is involved in parallel computing.

Why would MS accept a transitional apu design that simply acting as a bridge between AMD early immature designs and a full HSA implementation.

The PS4 isn't "based on kabini". The only relation between the two is that they contain jaguar cores.
AMD never said that a design using jaguar cores can't support hUMA, they said kabini (a chip, not an architecture) doesn't support it.

Well there is a lot more in common with Kabini and the APUs in the new consoles that just x86 core architecture. But you are correct that because Kabini doesn't have it does NOT mean that these custom SoCs will not have something similar at the least.

In your article you say more stream processors means more powerful. That is not true.
An example is that people are speculating The Ps4 as a 7850 Pitcairn and XB1 as a 7790 Bonaire. what they are failing to report is the 7850 Pitcairn is a 2012 gpu model, and the 7790 Bonaire is a 2013 model. If you look at the comparison chart the 7790 Bonaire is more powerful with less ram and less stream processors.
see chart http://en.wikipedia.org/wiki/Graphics_Core_Next
======================================
BONAIRE 7790 V PITCAIRN 7850
======================================
as we know many websites are saying XB1 Is using an HD 7790 Bonaire and that PS4 uses a 7850 Pitcarn. What they fail to mention is the 7790 is more powerful than the 7850 according to chart onhttp://en.wikipedia.org/wiki/Graphics_Core_Next
it also states
the 7850 Pitcarn had 2gb of ram against 7790 Bonaire 1gb of ram the bonaire out performs it with less ram and stream processors.

GFLOPS
128 BUS 7790 896 stream cores 1,792 GFLOP
256 BUS 7850 1024 usable stream cores 1,761 GFLOP
The 7790 Bonaire (march 2013)was released after the 7850 Pitcairn (march 2012)causing the Pitcairn to be discontinued.
--------------
Radeon HD 7800
Codenamed Pitcairn, the Radeon HD 7800 series was formally unveiled on March 5, 2012, with retail availability from March 19, 2012. Products include the Radeon HD 7870 and Radeon HD 7850. The Radeon HD 7870 features 1280 usable stream cores, whereas the Radeon HD 7850 has 1024 usable stream cores. Both cards are equipped with 2 GB GDDR5 memory and manufactured on TSMC's 28 nm process.[11]
---------------
Radeon HD 7700
Codenamed Cape Verde, the Radeon HD 7700 series was released on February 15, 2012. Products include the Radeon HD 7770 GHz Edition and Radeon HD 7750. The Radeon HD 7770 GHz Edition features 640 stream cores based on the GCN architecture, whereas the Radeon HD 7750 has has only 512 usable stream cores. Both cards are equipped with 1 GB GDDR5 memory and manufactured in 28 nm. On March 22, 2013 another card, Radeon HD 7790, was introduced in this series. This card is based on the Bonaire architecture, featuring 896 stream cores based on GCN 1.1 technology, an incremental update of GCN. After the introduction the Radeon HD 7790, AMD discontinued the Radeon HD 7850.

Now though I believe XB1 is based off Kaveri, it's just funny to see all over the web it seems none of these journalist or tech sites know that the 7790 Bonaire is a year newer and the replacement for the 7850 Pitcarn

First off, the GPU in the XBOX1 only has 768 shaders compared to the PS4's 1152 shaders, NOT 896 like in the 7790. Also, the PS4 has much higher memory bandwidth than the XBOX1, 68.3 GB/s on the XBOX1 compared to the PS4's 176 GB/s. Although the XBOX1 does have embedded memory which should help mitigate some of this massive difference in total bandwidth.

If you look at the chart on Anandtech's review, it explicitly states the peak shader throughput to be 1.23 TFLOPS on the XBOX and 1.84 TLFOPS on the PS4.

The reason why the 7790 has higher TFLOPS is due to clockspeed. It's clocked at 1GHz while the 7580 is only clocked at 860MHz. Even so, the 7850 has over 50% more memory bandwidth than the 7790 so it will still be faster in nearly every case. The pixel fillrate is also over 50% higher than the 7790 on the 7850.

dont say that word!!!!! It hurts me so, before newegg, before I knew better, bought a mother board for my new low end P4 to repalce a dead P3 board, Rambus only weeks before ddr won. Still makes me shudder going to the shop 3 weeks later wanting another 512m ram and hearing I had tippled in price and would take weeks to arrive. Please, never speak of rambus again, I never want to.

A few things here. HSA as a specification has not been ratified yet by the members. They are expecting that in 2014 or so. In the meantime, AMD defined hUMA so they can launch Kaveri. I would imagine that hUMA will become a subset of HSA, but for the time being that is the only official hUMA part coming out.

I had asked one of the fellows from AMD about the PS4/XBone chips being HSA compliant, and his response was, "They are not fully HSA compliant, but they do have some HSA features." So, saying that these parts will fully enable hUMA is taking a small leap. Sony and MS could embrace some features, but not fully implement them. My guess is that we will see a few hUMA type features, but not the full specification that we will see with Kaveri. Blame AMD/MS/Sony for your anger here, not Ryan. We work on what material we can dig up and verify.

Just calling something "shared memory" does not necessarily mean that it is unified memory for cross processor access (CPU/GPU). There is a lot of interesting information out there, none of it very clear right now.